An experimental study on the influence of trace impurities on ionization of atmospheric noble gas dielectric barrier discharges.

While the influence of trace impurities in noble gas discharges is well established in theoretical work, experimental approaches are difficult. Particularly the effects of trace concentrations of N2 on He discharges are complicated to investigate due to the fact that for He 5.0 the purity of He is only 99.999%. This corresponds to a residual concentration of 10 ppm, thereof 3 ppm of N2, in He. Matters are made difficult by the fact that He DBD plasmajets are normally operated under an ambient atmosphere, which has a high abundance of N2. This work tackles these problems from two sides. The first approach is to operate a DBD plasmajet under a quasi-controlled He atmosphere, therefore diminishing the effect of atmospheric N2 and making a defined contamination with N2 possible. The second approach is using Ar as the operating gas and introducing propane (C3H8) as a suitable substitute impurity like N2 in He. As will be shown both discharges in either He or Ar, with their respective impurity show the same qualitative behaviour.

Current density and conductivity dependent electroporation of Escherichia coli C600.

Transformation and surviving of E. coli C600 have been evaluated in dependence on the electric field strength and current density by changing the conductivity of the bacteria suspension. In this context the impact of making bacteria electrocompetent and the addition of NaCl solution was examined. Transformation efficiency declines with increasing conductivity of the suspension. When washing bacteria differently, the transformation efficiency correlates with the number of survivors. In contrary, adding different concentrations of NaCl has no effect on the surviving of E. coli C600. In dependence on the electric field strength, the transformation efficiency shows no effect on changing the conductivity. Regarding the transformation efficiency in dependence of the current density, a clear shift of the transformation maximum was observed. For higher conductivities, higher current densities are needed to reach the transformation maximum.

Process optimization and biocompatibility of cell carriers suitable for automated magnetic manipulation.

There is increasing demand for automated cell reprogramming in the fields of cell biology, biotechnology and the biomedical sciences. Microfluidic-based platforms that provide unattended manipulation of adherent cells promise to be an appropriate basis for cell manipulation. In this study we developed a magnetically driven cell carrier to serve as a vehicle within an in vitro environment. To elucidate the impact of the carrier on cells, biocompatibility was estimated using the human adenocarcinoma cell line Caco-2. Besides evaluation of the quality of the magnetic carriers by field emission scanning electron microscopy, the rate of adherence, proliferation and differentiation of Caco-2 cells grown on the carriers was quantified. Moreover, the morphology of the cells was monitored by immunofluorescent staining. Early generations of the cell carrier suffered from release of cytotoxic nickel from the magnetic cushion. Biocompatibility was achieved by complete encapsulation of the nickel bulk within galvanic gold. The insulation process had to be developed stepwise and was controlled by parallel monitoring of the cell viability. The final carrier generation proved to be a proper support for cell manipulation, allowing proliferation of Caco-2 cells equal to that on glass or polystyrene as a reference for up to 10 days. Functional differentiation was enhanced by more than 30% compared with the reference. A flat, ferromagnetic and fully biocompatible carrier for cell manipulation was developed for application in microfluidic systems. Beyond that, this study offers advice for the development of magnetic cell carriers and the estimation of their biocompatibility.

Dielectric barrier discharges in analytical chemistry.

The present review reflects the importance of dielectric barrier discharges in analytical chemistry. Special about this discharge is-and in contrast to usual discharges with direct current-that the plasma is separated from one or two electrodes by a dielectric barrier. This gives rise to two main features of the dielectric barrier discharges; it can serve as dissociation and excitation device and as ionization mechanism, respectively. The article portrays the various application fields for dielectric barrier discharges in analytical chemistry, for example the use for elemental detection with optical spectrometry or as ionization source for mass spectrometry. Besides the introduction of different kinds of dielectric barrier discharges used for analytical chemistry from the literature, a clear and concise classification of dielectric barrier discharges into capacitively coupled discharges is provided followed by an overview about the characteristics of a dielectric barrier discharge concerning discharge properties and the ignition mechanism.

Electronic coupling and scaling effects during dielectric barrier electrospray ionization.

The mechanism of the previously published technique of dielectric barrier electrospray ionization (DB-ESI) was investigated in more detail. Two independent current signals occurring during the DB-ESI could be explained and allocated to sub-processes. The modulated shape of the HV signal, the applied frequency as well as the inner diameter of the emitter capillary have a big impact on the spray. Furthermore, there exists a cut-off frequency which depends on the electronic properties of the DB-ESI interface. Comparable mass spectra for lysine employing both conventional ESI and DB-ESI show a good analytical potential of the new technique.

The micro-discharge family (dark, corona, and glow-discharge) for analytical applications realized by dielectric barriers.

The similarity principles of electric plasmas, and the current-voltage characteristics of the most prominent kinds of discharges used for analytical applications, are discussed. Most of the discharges can be miniaturized, and some of the analytical applications of different discharges can be realized by use of dielectric barriers for analytical applications, for example element spectrometry, as an ionization source for ion-mobility spectrometry or organic mass spectrometry, and as an electrospray ionization source.

Electrical generators driving microhollow and dielectric barrier discharges applied for analytical chemistry.

Scaling down the size of plasma discharges would reduce the amount of gases, liquids, and consumables required, which in turn would decrease the operating costs. Nevertheless, the application of a specialized plasma generator for microhollow cathode discharges (MHCD) and dielectric barrier discharges are driven with commercially available power sources. Those generators are bulky and expensive and their overall efficiency is poor. This work develops and explains several circuit topologies and design hints to excite MHCD and dielectric barrier discharge (DBD) plasmas with respect to its system with as low as possible input power in a very efficient way. Benefits in sensitivity and life expectancy are shown. The generator for the MHCD needs voltages up to 7 V and consumes up to 5 W. The DBD generator has an input power of 3 W and produces a fast rising output pulse up to 9 kV, which has a time duration of 2 micros. These low-power circuits offer the operation with batteries.

Microplasma-based atomic emission detectors for gas chromatography.

This paper is an update on the development of microplasmas as detectors for gas chromatography. Direct current (dc), alternating current (ac), and radio frequency (rf) microplasmas developed in recent years will be described with their significant analytical results, which mostly concern the detection of halogens and sulfur. New results will be added which employ a microhollow cathode discharge (MHCD) as excitation source. Emphasis will be given to this microplasma which has already been implemented as an element-selective detector for emission spectrometry and as ionization source for mass spectrometry. The possibility to use it as a multielement-selective detector for gas chromatography will be presented. A discussion of the published detection limits of all these microplasmas is given.

Element selective detection of molecular species applying chromatographic techniques and diode laser atomic absorption spectrometry.

Tunable diode laser atomic absorption spectroscopy (DLAAS) combined with separation techniques and atomization in plasmas and flames is presented as a powerful method for analysis of molecular species. The analytical figures of merit of the technique are demonstrated by the measurement of Cr(VI) and Mn compounds, as well as molecular species including halogen atoms, hydrogen, carbon and sulfur.

Laser atomic absorption spectrometry of excited Hg in a discharge applying sum frequency mixing of two diode lasers (preliminary results).

Wavelength modulation diode laser atomic absorption spectrometry is applied to the detection of atomic mercury. Transitions from metastable energy levels highly populated in a radio-frequency discharge are induced with laser diodes by use of nonlinear techniques. The wavelength of one strong transition at 365.119 nm with a high oscillator strength is obtained by sum frequency generation of two diode lasers. The cold vapor technique is used to transfer ionic into atomic mercury. The mercury in the vapor phase is transported by an argon stream into the discharge tube. From the time-dependent absorption signals detection limits of 100 ng/L are achieved at this state of research.

Effect of heat on induction and repair of DNA strand breaks in X-irradiated CHO cells.

Chinese hamster ovary cells were exposed to various heat treatments followed by X-irradiation, and the induction and repair of DNA strand breaks was studied using the alkaline unwinding technique. Heat treatments alone were found to cause DNA strand breakage only for temperatures greater than or equal to 43 degrees C, whereas the number of radiation-induced strand breaks was unaffected by additional heating. Strand break repair was studied for irradiated cells preheated at temperatures ranging from 42 degrees C to 45 degrees C. The total repair curve could be separated into three phases, a fast (t = 0-15 min), an intermediate (t = 15-120 min) and a slow (t greater than or equal to 120 min) phase. All phases were altered when cells were heated either prior to or after irradiation. The fast and the intermediate phase could be well interpreted by the assumption that irradiation leads to both primary and secondary single-strand breaks, the latter being generated by enzymatic incision at sites of damaged bases. For irradiation alone, the ratio of all secondary strand breaks to all primary breaks was fsec = 1.5 +/- 0.5. This ratio was not altered by preceding heat treatments (mean fsec = 1.7 +/- 0.2). The main effect of heating on the repair kinetics of single-strand breaks was an increase in the repair half-time of primary and secondary breaks (maximum increase by a factor of 3.4), whereas the generation of secondary breaks was only slightly retarded (factor 1.3). The slow repair phase, which is assumed to represent the repair of DNA double-strand breaks, was best described by a single exponential component. The half-time of this component was found to increase from tau slow = 170 +/- 70 min for non-heated cells to tau slow = 345 +/- 80 min for cells heated at 45 degrees C for 20 min, indicating that heat inhibited the repair of double-strand breaks. For irradiation alone, the initial fraction of the slow component was fslow = 0.065 +/- 0.004. This fraction was enhanced by additional heating, with a maximum increase by a factor of 2.7 for cells heated at 45 degrees C for 20 min. This elevation cannot be the result of an enhanced induction of double-strand breaks, but must be associated with an additional formation of slowly repaired strand breaks during repair incubation. These additional strand breaks must arise from strand breaks which in non-heated cells are repaired during the fast or intermediate phase.(ABSTRACT TRUNCATED AT 400 WORDS)

DNA denaturation kinetics in CHO cells exposed to different X-ray doses and after different repair intervals using the alkaline unwinding technique.

The kinetics of DNA denaturation in alkaline solution (pH 12.2) was studied in CHO cells using the alkaline unwinding technique. After X-ray doses of 0, 3, 5 and 9 Gy, the kinetics of alkaline denaturation was found to be independent of the number of induced strand breaks confirming earlier studies on this subject. In addition, the denaturation kinetics measured in cells exposed to 9 Gy were found to be identical for different repair intervals. This result shows that for the three different classes of DNA strand breaks described previously (Dikomey and Franzke 1986a) strand separation in alkaline solution occurs at the same kinetics. As a consequence, the relationship between the numbers of strand breaks and the fraction of remaining double-stranded DNA is considered the same for the three different classes.

Three classes of DNA strand breaks induced by X-irradiation and internal beta-rays.

Repair kinetics of DNA strand breaks were investigated after exposing exponentially growing CHO cells to X-radiation or to internal beta-rays from incorporated tritium, respectively. DNA strand breaks were analysed by the alkaline unwinding technique followed by chromatography on hydroxyapatite. For either type of radiation, the repair kinetics are statistically best described by a sum of three exponential components. The half-times determined are tau I approximately 2 min, tau II approximately 20 min and tau III approximately 170 min; they are identical for both types of radiation. But the initial fractions of the components are different for X- and internal beta-rays; X-rays; fI = 0.70, fII = 0.25, fIII = 0.05; internal beta-rays: fI = 0.40, fII = 0.40, fIII = 0.20. Components I and II are considered to represent the repair of two different classes of single-strand breaks and component III the repair of double-strand breaks. Two alternative interpretations for the occurrence of the two classes of single-strand breaks are discussed.

DNA repair kinetics after exposure to X-irradiation and to internal beta-rays in CHO cells.

DNA strand breaks induced by X- or internal beta-rays were measured using the alkaline unwinding technique. For either type of radiation, repair kinetics were found to be best described by three exponential components, the half-times of which are 2 min, 17 min and 200 min, respectively. These values are the same for X- and internal, beta-irradiation but the initial fractions of the components are different.